Subterranean heaters have been used to heat subterranean geological formations in oil production, remediation of contaminated soils, accelerating digestion of landfills, thawing of permafrost, gasification of coal, as well as other uses. Some examples of subterranean heater arrangements include placing and operating electrical resistance heaters, microwave electrodes, gas-fired heaters or catalytic heaters in a bore hole of the formation to be heated. Other examples of subterranean heater arrangements include circulating hot gases or liquids through the formation to be heated, whereby the hot gases or liquids have been heated by a burner located on the surface of the earth. While these examples may be effective for heating the subterranean geological formation, they may be energy intensive to operate.
U.S. Pat. Nos. 6,684,948 and 7,182,132 propose subterranean heaters which use fuel cells as a more energy efficient source of heat. The fuel cells are disposed in a heater housing which is positioned within the bore hole of the formation to be heated. The fuel cells convert chemical energy from a fuel into heat and electricity through a chemical reaction with an oxidizing agent. U.S. Pat. No. 7,182,132 teaches that in order to start operation of the heater, an electric current may be passed through the fuel cells in order to elevate the temperature of the fuel cells sufficiently high to allow the fuel cells to operate, i.e. an electric current is passed through the fuel cells before the fuel cells are electrically active. While passing an electric current through the fuel cells may elevate the temperature of the fuel cells, passing an electric current through the fuel cells before the fuel cells are electrically active may be harsh on the fuel cells and may lead to a decreased operational life thereof.
U.S. patent application Ser. No. 14/013,708 to Fischer et al., the disclosure of which is incorporated herein by reference in its entirety, teaches a subterranean heater which uses fuel cells and combustors to heat a geological formation. The fuel cells and combustors are disposed in a heater housing in an alternating pattern and are operated to heat the heater housing, and consequently the geological formation. U.S. patent application Ser. No. 14/013,879 to Haltiner et al., the disclosure of which is incorporated herein by reference in its entirety, teaches a subterranean heater which uses fuel cells to heat a geothermic formation where an arrangement of electric resistance heating elements are used to elevate the temperature of the fuel cells from an inactive temperature to an active temperature. While using electric resistance heating elements may be effective to elevate the temperatures of the fuel cells from the inactive temperature to the active temperature, the electric resistance heating elements may add cost and complexity to the system.
What is needed is a heater which minimizes or eliminates one of more of the shortcomings as set forth above.